1. Field of the Invention
The present invention relates to a process for producing 3-methyltetrahydrofuran, which is an extremely useful substance that is utilized as a comonomer for modifying poly(tetramethylene ether glycol) obtained by polymerizing tetrahydrofuran. [Refer to Japanese Patent Application Laid-Open No. 235320/1988 (Sho-63) and European Patent Application Laid-Open No. 343985].
2. Description of the Related Arts
As a process for producing 3-methyltetrahydrofuran, Japanese Patent Application Laid-Open No. 219981/1994 (Hei-6) describes the process for producing 2-methyl-1,4-butane-diol and 3-methyltetrahydrofuran by the hydrogenation of an itaconic acid ester or a 3-formyl-2-methylpropionic acid ester, and also Japanese Patent Application Laid-Open No. 217768/1996 (Hei-8) describes the process for producing 3-methyltetrahydrofuran by the hydrogenation of a methyl-succinic acid ester. However, when an attempt is made to produce 3-methyltetrahydrofuran by the use of the above-mentioned ester as a starting raw material, it is inevitable that the reaction product contains an alcohol as well as the objective 3-methyltetrahydrofuran. 3-Methyltetrahydrofuran forms an azeotropic mixture with most of the lower alcohols, for example, with methanol, forming an azeotropic mixture having an azeotropic point of 64.5.degree. C. and an azeotropic composition consisting of 25% by weight of 3-methyltetrahydrofuran and 75% by weight of methanol, thus it requires a large amount of energy to separate 3-methyltetrahydrofuran from the azeotropic mixture. In particular, the 3-methyltetrahydro-furan which is employed for modifying poly(tetramethylene glycol) is required to have highly purity and to have contents of alcohols not more than 0.2%